The present invention relates to a novel polymerizable emulsifying agent, and more particularly relates to a novel polymerizable emulsifying agent providing an aqueous emulsion polymerization process for .alpha.,.beta.-ethylenically unsaturated monomer which does not discharge an environmental pollutant such as emulsifying agent, water-soluble polymeric material, water-soluble oligomer or oil-soluble oligomer in such a step as filtration or washing of polymer by polymerizing the polymerizable emulsifying agent and the specific .alpha.,.beta.-ethylenically unsaturated monomer polymerizable therewith.
The present invention further relates to a novel polymerizable emulsifying agent which is polymerized with acrylonitrile to provide a modacrylic fiber superior in heat stability and fastness to light.
The polymerizable emulsifying agent of the present invention is sulfoalkyl-alkylmaleates having one hydrophobic alkyl group and one hydrophilic sulfoalkyl group which is prepared from maleic anhydride, higher alcohol and one of propanesultone, butanesultone, sodium 2-oxy-ethanesulfonate and sodium isethionate. The polymerizable emulsifying agent of the invention is effectively employed in a polymerization of .alpha.,.beta.-ethylenically unsaturated monomer so as to prevent discharge of environmental pollutants by industrial wastes, also effectively employed for improving properties such as heat stability, mechanical property, transparency and processing property of synthetic resins such as copolymer of acrylonitrile and others.
An aqueous emulsion polymerization process has been utilized to prepare a polymerized material in a field such as synthetic rubber, synthetic resin, coating material or synthetic fiber. In such a process, after polymerization, the polymerized material is taken out as an intermediate product or a product through steps such as filtration from an aqueous medium, washing and drying, and frequently environmental pollutants such as water-soluble polymeric material, water-soluble or oil-soluble oligomer, which are by-produced in polymerization, as well as emulsifying agent are discharged into drainage at the time of filtration or washing of a polymerized material. In recent years, the recognition concerning toxicity of emulsifying agent becomes deepened, and also a water-soluble polymeric material and a water-soluble or oil-soluble oligomer may pollute water since they are pollutants being capable of giving chemical oxygen demand (COD) load and biological oxygen demand (BOD) load which exhaust a large amount of oxygen dissolved in water when they are decomposed by microorganisms. A water pollution such as sea water area, rivers, lakes and marshes or public water area has recently constituted a serious social problem as one of an environmental pollutants, and a countermeasure against a polymerization drainage as stated above has been strongly desired.
Hitherto, an aqueous emulsion polymerization process has been utilized in preparation of various polymers with industrial advantages that it produces less scale or coagula in comparison with another aqueous polymerization process, reaction heat in polymerization is readily removed and polymerization reaction can be stably carried out even at high monomer concentration.
However, a conventional emulsifying agent is not polymerizable and it is merely adsorbed on a surface of polymer particle. Then various unfavorable things arise since it does not bond chemically to a polymer. For instance, in case of processing a polymer to shaped article such as film, fiber, or the like, an emulsifying agent must be removed off completely from polymer since an emulsifying agent remaining in polymer makes the properties such as transparency, heat stability, mechanical property, fastness to light and water resistance worse. For the removal of an emulsifying agent, a large amount of wash water must be employed, which is still insufficient.
On the other hand, there has been known a polymerizable aninonic emulsifying agent, for instance, sulfo ester of .alpha.-methylene carboxylic acid derivatives such as sodium 2-sulfoethyl-.alpha.-methylacrylate, sodium 2-sulfoethyl-.alpha. -butylacrylate and sodium 2-sulfoethyl-.alpha.-hexylacrylate, monoalkylitaconoxypropanesulfonate derivatives such as potassium monolaurylitaconoxypropanesulfonate and sodium monocetyilitaconoxypropanesulfonate, sodium p-styrelundecanoate, sodium 10-acrylamidestearate or sodium 10-acryloxystearate. These polymerizable emulsifying agents contribute to improve the mechanical stability and the pigment dispersion of latex, or the wet strength, the water resistance and the adhesiveness of film or coated material. However, in case of recovering a polymer from latex prepared by employing the above-mentioned emulsifying agent through passing the salting-out, filtration, washing and drying to give the desired polymer, the employment of such an emulsifying agent reveals the following defects at the time of polymerization. For instance, in case of polymerizing .alpha.,.beta.-ethylenically unsaturated monomer by employing a sulfo ester of .alpha.-methylene carboxylic acid derivatives or monoalkylitaconoxypropanesulfonate derivatives as a polymerizable emulsifying agent, a homopolymer of the polymerizable emulsifying agent, or a water-soluble copolymer or a liquid oligomer which is abundant in the polymerizable emulsifying agent is apt to be by-produced since such a polymerizable emulsifying agent is readily homopolymerized or copolymerized. In case of polymerizing an .alpha.,.beta.-ethylenically unsaturated monomer by employing a polymerizable emulsifying agent such as sodium 10-acrylamidestearate or sodium 10-acryloxystearate, a homopolymer of the polymerizable emulsifying agent is apt to be by-produced or the unreacted polymerizable emulsifying agent is apt to remain comparatively in large quantities since such a polymerizable emulsifying agent is readily homopolymerized but hardly copolymerized. These by-products and the residue are abundantly discharged together with a drainage because they are difficult to recover. Therefore, such conventional polymerizable emulsifying agents also have the disadvantage in the point of environmental pollution though they are effective in improving properties as mentioned above.
Furthermore, there has been known as acrylonitrile copolymer for modacrylic fiber, especially the copolymer containing 30 to 80 % by weight of acrylonitrile, which is prepared by an aqueous emulsion polymerization process employing a usual emulsifying agent. However, such a copolymer contains a small amount of emulsifying agent even though water wash is completed as much as possible on industrial scale, and a modacrylic fiber prepared therefrom is inferior in heat stability and fastness to light due to the residual emulsifying agent. Therefore, commercial value of modacrylic fiber has been discounted in spite of its excellent properties such as flame resistance, high bulkiness, lusterness and hand touchness. For the purpose of decreasing the residual amount of emulsifying agent in the copolymer, the present inventors have carried out an emulsion polymerization by employing the aforementioned known polymerizable emulsifying agent. However, it has been found out that heat stability and fastness to light are not improved though the employed polymerizable emulsifying agent is copolymerized with acrylonitrile to be bonded chemically within the polymer molecule. Besides, under certain circumstances, softening temperature of the copolymer was lowered as a result of introducing a substituent group which is bulky in excess as a side-chain of the copolymer by means of copolymerizing an polymerizable emulsifying agent. As such examples, monoalkylitaconoxypropanesulfonate derivatives such as sodium monolaurylitaconoxypropanesulfonate are mentioned.